In communication devices where a transmit path and a receive path share the same antenna, an intermediate device (e.g. a duplexer) may be provided to connect the transmit path and the receive path to the antenna. For example, a duplexer may separate different frequency bands used for transmission and reception of radio frequency signals by means of frequency-selective filter elements. For example, a first frequency band may be used by the transmit path for transmitting radio frequency signals, whereas a second frequency band may be used by the receive path for receiving radio frequency signals. A distance between a frequency band for transmission and a frequency band for reception is called “duplex distance”. For example, a duplex distance may be 30 MHz for Long Term Evolution (LTE) frequency band 17. In particular, the transmit path and the receive path may be operated simultaneously, i.e., in Frequency-Division Duplexing (FDD) mode.
A duplexer should provide an adequate rejection of signal components related to transmission within a frequency band for reception. However, when a transmission signal is provided to the duplexer, leakage to the frequency band used for signal reception may occur. Thus, an undesired leakage component may be caused in a receive signal and yield significant transmit power in the receive signal. Accordingly, a signal containing a desired receive signal component and the undesired leakage component related to a baseband transmit signal may be provided to a subsequent receiver which may even result with the desired receive signal component being unrecoverable. Apart from leakage, there may also be other processes causing undesired components in a receive signal provided to a receiver (e.g. a blocker signal).
InterModulation Distortions (IMD) may be generated by a mixer of the receiver receiving a signal having different frequency components. For example, unwanted signal components may be present within a baseband receive signal generated by a mixer resulting from the non-linearity of the same. Referring to the above example, signal components having a frequency related to the sum or the difference of frequencies of the desired receive signal component and the undesired leakage component input to the mixer may be present in the baseband receive signal generated by a mixer. In this event, the generated undesired signal components are referred to as second order IMD components. The second order IMD components may lower a Signal-to-Noise Ratio (SNR) of the baseband receive signal.
For Carrier Aggregation (CA), a receiver may comprise a single receive path for each component carrier and multiple clock domains may be used in the receiver (e.g. a dedicated local oscillator signal for a mixer of the respective receive path). Due to intermixing of frequencies from the multiple clock domains, a spur may occur at the mixer of a receive path. A spur is an undesired signal component occurring in addition to the dedicated local oscillator signal at an input of the mixer (e.g. due to crosstalk between the receive paths). Depending on the chosen carrier frequencies, the spur may have a frequency which is similar to a frequency of the undesired leakage component. Accordingly, the mixer may down-mix the undesired leakage component to the baseband due to the spur. The down-mixed leakage component may overlap with the down-mixed desired receive signal component and degrade the SNR of the baseband receive signal.
Conventional approaches attempt to mitigate the above described effects by suppressing the undesired leakage component before they can reach the mixer. In order to achieve this, a higher attenuation of the duplexer or separate flexible Surface Acoustic Wave (SAW) filters which filter out the undesired leakage component may be used. However, conventional approaches using analog technique require a large amount of space on a semiconductor substrate carrying the receiver. Also, the approach is not adapting to varying environmental conditions and aging of the used components so that the extent of improvement may end up being erratic. Furthermore, the (additional) high quality analog components increase manufacturing costs. Hence, there may be a desire for improved reduction of distortion components within a baseband receive signal